Coaxial cable antenna for communication with implanted medical devices

ABSTRACT

In general, the invention is directed to a coaxial cable antenna for use in an external device, such as a programmer or monitor, to enhance communication between the external device and an implanted medical device (IMD). The coaxial cable antenna provides the external device with polarization diversity. For example, the coaxial cable antenna includes a first portion and a second portion that are substantially perpendicular to one another. Each of the portions of the coaxial cable antenna has a different polarization orientation, thus providing the programmer with polarization diversity. Further, the external device may include more than one coaxial cable antenna to provide the external device with spatial diversity as well as polarization diversity provided by the coaxial cable antenna design. The coaxial cable antenna configurations reduce problems associated with polarization mismatches, antenna nulls, and multi-path propagation interference.

CROSS-REFERENCE TO PRIOR APPLICATION

This application is a continuation application of prior application Ser.No. 11/199,109, filed Aug. 8, 2005, entitled “Coaxial Cable Antenna forCommunication with Implanted Medical Devices,” now allowed; which is acontinuation of U.S. Pat. No. 6,930,602, filed Apr. 25, 2003, entitled“Coaxial Cable Antenna for Communication with Implanted MedicalDevices.”

TECHNICAL FIELD

The invention relates to wireless communication between an implantedmedical device (IMD) and an external programmer or monitor and, moreparticularly, to antennas for use with the external programmer ormonitor.

BACKGROUND

An implanted medical device (IMD) and an external device, such as aprogrammer or monitor, exchange information via wireless communication.For example, the external device typically transmits commands to theIMD. In addition, the IMD transmits stored information or sensedphysiological parameters to the external device.

The external device typically includes a programming head containing anantenna for wireless communication with an antenna in the IMD. Inoperation, the programming head is placed in close proximity to the IMDto establish data communication with the IMD.

SUMMARY

In general, the invention is directed to a coaxial cable antenna for usein an external device, such as a programmer or monitor, to enhancecommunication between the external device and an implanted medicaldevice (IMD).

In accordance with the invention, the external device includes twocoaxial cable antennas for communication with the IMD. The coaxial cableantenna is constructed to provide polarization diversity, which allowsthe antenna to operate effectively in different planes. In order toachieve polarization diversity, the two antennas are arranged orthogonalto one another. The external device includes the two coaxial cableantennas to provide the external device with spatial diversity as wellas polarization diversity provided by the coaxial cable antenna design.For example, a programmer for an IMD includes a first coaxial cableantenna, a second coaxial cable antenna, and a receiver that receivessignals from the IMD via one of the first or the other coaxial cableantennas. The programmer includes a display, and the coaxial cableantennas are mounted within a housing of the display to protect thecoaxial cable antennas from the surrounding environment. In other words,the display housing is part of and protects the coaxial cable antennasfrom incidental contact that could otherwise bend or break the antennas.

The coaxial cable antennas can be mounted proximate upper corners of thedisplay. Specifically, the first coaxial cable antenna is locatedproximate a top left corner of the display and the second coaxial cableantenna is located proximate a top right corner of the display. Each ofthe coaxial cable antennas includes a first portion substantiallyparallel to a side of the display and a second portion substantiallyparallel to a top of the display. The portion of each coaxial cableantennas parallel with the side of the display has a first polarizationand the portion of each coaxial cable antennas parallel with the top ofthe display has a second polarization. In other words, each of theportions of the coaxial cable antennas has a different polarizationorientation, thus providing the programmer with polarization diversity.

In addition, the coaxial cable antennas are spaced approximately half ofa wavelength apart from one another to achieve spatial diversity.However, the coaxial cable antennas could be spaced approximatelyone-quarter of a wavelength apart from one another. In this manner, thecoaxial cable antennas receive signals from the IMD over multipledifferent receive paths providing a programmer or monitor with spatialdiversity as well as the polarization diversity provided by the coaxialcable antenna design.

Each of the coaxial cable antennas includes a center conductor thatcarries signals received from the IMD or signals to be transmitted tothe IMD, surrounded by an insulator and an outer conductive claddingsurrounding the center conductor. In accordance with the invention, aportion of the outer conductive cladding is removed to expose theinsulator of the coaxial cable antenna.

The portion of the removed outer conductive cladding is located near amidpoint of the coaxial cable antennas. Further, a portion of theexposed insulator is removed to expose the center conductor of coaxialcable antennas. A resistor and a capacitor are connected between thecenter conductor and the outer conductive cladding.

The capacitor is connected between the center conductor and the outerconductive cladding in order to adjust the voltage standing wave ratio(VSWR) at an operating frequency of the coaxial cable antennas. Theresistor is also connected between the center conductor and the outerconductive cladding to lower the quality factor (Q) of the coaxial cableantennas, in turn, increasing the bandwidth of the coaxial cableantennas.

Each coaxial cable antenna further includes a hole that extends throughthe outer conductive cladding and cuts through the center conductor at aspecific location to tune the operating frequency of the coaxial cableantenna. The hole may be placed such that the operating frequency of thecoaxial cable antennas tune to approximately 400 Megahertz (MHz) and,more specifically, approximately 403 MHz.

In one embodiment, the invention provides an external device thatcommunicates with an implanted medical device, the external devicecomprising a first coaxial cable antenna, a second coaxial cableantenna, and a receiver that receives signals from the implanted medicaldevice via at least one of the first and second coaxial cable antennas.

In another embodiment, the invention is directed to an external devicethat communicates with an implanted medical device, the external devicecomprising a plurality of coaxial cable antennas, a receiver to receivesignals from the implanted medical device via at least one of thecoaxial cable antennas, and a device housing, the coaxial cable antennasmounted within the device housing.

In a further embodiment, the invention is directed to a methodcomprising receiving signals from an implanted medical device via aplurality of coaxial cable antennas and processing the signals from theimplanted medical device to analyze information from the implantedmedical device.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other advances andinventive aspects of the invention will be apparent from the descriptionand drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective diagram illustrating an external device thatcommunicates with an implantable medical device (IMD) implanted within apatient.

FIG. 2 is a block diagram illustrating the programmer of FIG. 1 ingreater detail.

FIG. 3 is a schematic diagram illustrating a display of a programmerwith a front portion of a housing removed to illustrate an interior ofthe display.

FIG. 4 is a schematic diagram illustrating a coaxial cable antenna inaccordance with the invention.

DETAILED DESCRIPTION

FIG. 1 is a perspective diagram illustrating an external device, e.g., aprogrammer 10, that communicates with an implantable medical device(IMD) 12 implanted within a patient 14. In accordance with theinvention, programmer 10 includes coaxial cable antennas 16A and 16B(hereinafter 16) arranged to provide programmer 10 with spatial as wellas polarization diversity. Programmer 10 transmits commands to IMD 12and receives stored operational information and physiologicalinformation from IMD 12.

IMD 12 may be an implantable pulse generator (IPG), e.g., a pacemaker,or an implantable cardioverter-defibrillator (ICD). However, programmer10 may be used to communicate with any type of IMD 12. Other examples ofIMD 12 include an implantable brain stimulator, an implantable gastricsystem stimulator, an implantable nerve stimulator or muscle stimulator,an implantable lower colon stimulator, urinary tract stimulator, animplantable drug or beneficial agent dispenser or pump, an implantablecardiac signal loop or other type of recorder or monitor, an implantablegene therapy delivery device, an implantable incontinence prevention ormonitoring device, an implantable insulin pump or monitoring device, andthe like.

Further, although described in terms of a programmer 10 for purposes ofillustration, the antenna configurations described herein may be used inother external devices that communicate with an IMD 12 such as a patientmonitoring device, which may not have programming capabilities. In eachcase, the external device communicates with IMD 12 to obtain operationaland physiological information. IMD 12 collects operational informationand physiological information. Depending on the type of IMD 12, thephysiological information may include heart rate, heart ratevariability, blood glucose levels, oxygen saturation, partial pressureof oxygen in the blood, blood pressure, baro-reflex measures,electrogram morphologies, lung wetness, and the like.

A user (not shown) of programmer 10, such as a clinician or physician,interacts with programmer 10 and IMD 12 via an input medium, such askeyboard 18, and a display 20. More specifically, programmer 10 providesa user interface that the user interacts with to provide data toprogrammer 10. Display 20 may for example, be a Cathode Ray Tube (CRT)display, Liquid Crystal Display (LCD), Light-Emitting Diode (LED)display, a plasma display or the like. In some embodiments, programmer10 also includes a pointing device, such as a mouse, via which the userinteracts with the user interface. Further, programmer 10 may include atouch screen or other similar input medium to interact with the user.

Programmer 10 is in wireless communication with IMD 12. Programmer 10communicates with IMD 12 by wireless transmission via coaxial cableantennas 16, constructed in accordance with the invention. Coaxial cableantennas 16 are mounted within a housing 24 of display 20 to protectcoaxial cable antennas 16 from the surrounding environment. In otherwords, housing 24 of display 20 prevents coaxial cable antennas 16 fromincidental contact that may otherwise bend or break antennas external toprogrammer 10. In some embodiments, coaxial cable antennas 16 may beexternal coaxial cable antennas coaxial cable antennas connected toprogrammer 10 via a cable. Housing 24 to which coaxial cable antennas 16are mounted is fabricated from a non-conductive material, such asplastic. Display 24 also includes a conductive backplane that isconstructed of a metal or metalized plastic. As will be described,coaxial cable antennas 16 are arranged to provide spatial diversity aswell as polarization diversity, in turn allowing programmer 10 tocommunicate with IMD 12 from several feet or meters away. Coaxial cableantennas 16 reduce problems associated with polarization mismatches,antenna nulls, and multi-path interference.

Programmer 10 interrogates IMD 12 to retrieve measured data, along withcurrently programmed parameters and optimization target values stored byIMD 12 via coaxial cable antennas 16. If IMD 12 is a pacemaker, the dataretrieved includes data reflecting electrical activity sensed in heart22, the output of various other sensors of IMD 12, such as one or moresensors used to control the rate response of IMD 12, and the rateresponse of IMD 12 over time. Programmer 10 displays some or all ofthese items to the user via display 20. The user further programs orreprograms IMD 12 via the user interface and input medium, e.g.,keyboard 18. For example, the user provides or adjusts rate responseparameters or target values of IMD 12 via the user interface and inputmedium, which are then relayed by programmer 10 to IMD 12 via atransmitter and coaxial cable antennas 16.

FIG. 2 is a block diagram illustrating programmer 10 in greater detail.As shown in FIG. 2, programmer 10 includes a processor 30, a radiofrequency (RF) module 31, an antenna switch 33 controlled via a receivedsignal strength indicator (RSSI) 35 and coaxial cable antennas 16A and16B (hereinafter 16). As mentioned above, programmer 10 is in wirelesscommunication with IMD 12. Particularly, programmer 10 transmits andreceives signals to and from IMD 12 via coaxial cable antennas 16.Coaxial cable antennas 16 are spaced substantially half of a wavelength,but could work with one quarter of a wavelength, from one another toreceive signals from IMD 12 over multiple receive paths providingprogrammer 10 with receive diversity, thereby reducing multi-pathpropagation interference as well as antenna nulls. For example, coaxialcable antenna 16A provides a first receive path and coaxial cableantenna 16B provides a second receive path. More than two coaxial cableantennas 16 may be provided in some embodiments for enhanced receivediversity.

Programmer 10 selects, via antenna switch 33 and RF module 31, thereceive path with the strongest signal. More specifically, RF module 31includes a receiver 32 and RSSI 35 that selects the receive path withthe strongest signal. Processor 30 receives data collected by IMD 12 andcurrently programmed parameters from IMD 12 via receiver 32 and one ofcoaxial cable antennas 16 and processes the data. RF module 31 furtherincludes a transmitter 34, which allows programmer 10 to program IMD 12,e.g., to program new parameters and/or optimization target values of IMD12, via coaxial cable antennas 16. Programmer 10 transmits signals toIMD 12 via one of coaxial cable antennas 16. Although in the exampleillustrated in FIG. 2 RF module 31 includes distinct components forreceiving and transmitting signals, i.e., receiver 32 and transmitter34, RF module 31 may include a single transceiver component thatincludes receive circuitry as well as transmit circuitry.

As discussed above, programmer 10 provides a user interface 36 by whicha user of programmer 10, such as a clinician or physician, interactswith programmer 10 and IMD 12. In the example of FIG. 2, user interface36 is a graphical user interface (GUI) displayed on display 20. A userinteracts with user interface 36 via display 20 and at least one inputmedium such as keyboard 18, a pointing device, e.g., mouse, or a touchscreen. A memory 38 stores program code that causes processor 30 todrive user interface 36, and the functionality ascribed to userinterface 36. Memory 38 may include any fixed or removable magnetic oroptical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks,EEPROM, or the like.

FIG. 3 is a schematic diagram illustrating display 20 with a frontportion of housing 24 removed to illustrate the interior of display 20.Display 20 includes coaxial cable antennas 16A and 16B (hereinafter 16),connectors 42A and 42B (hereinafter 42), and a casting 44. As describedabove, coaxial cable antennas 16 are located within non-conductivehousing 24 to protect coaxial cable antennas 16 from inadvertent damagecaused by the surrounding environment. In some embodiments, coaxialcable antennas 16 are attached to housing 24 via one or more fasteners.Housing 24 further covers casting 44 to protect casting 44 from thesurrounding environment. As described above, housing 24 is constructedfrom a non-conductive material such as plastic. In some embodiments,casting 44 is constructed of a conductive material, e.g., metal, andelectromagnetically couples to coaxial cable antennas 16 in order to aidin tuning and impedance matching.

As illustrated in the example of FIG. 3, coaxial cable antennas 16 aremounted proximate top corners of display 20. Specifically, coaxial cableantenna 16A is located proximate a top left corner of display 20 andcoaxial cable antenna 16B is located proximate a top right corner ofdisplay 20. Coaxial cable antennas 16 are substantially L-shaped to fitin the respective corners of display 20 and produce polarizationdiversity as described herein. In other words, each of coaxial cableantennas 16 includes a first portion 46 substantially parallel to a sideof display 20 and a second portion 48 substantially parallel to a top ofdisplay 20 in accordance with the invention. Portion 46 of coaxial cableantennas 16 has a first polarization and portion 48 of coaxial cableantennas 16 has a second polarization. More specifically, portion 46 ofcoaxial cable antennas 16 has a horizontal elliptical or circularpolarization (indicated by arrow 52), while portion 48 of coaxial cableantennas 16 has a vertical elliptical or circular polarization(indicated by arrow 54). In this manner, coaxial cable antennas 16provide programmer 10 with polarization diversity. In other words,programmer 10 and, more particularly coaxial cable antennas 16, receiveand transmit signals with horizontal polarization as well as verticalpolarization, thus reducing antenna pattern nulls due to polarizationmismatches.

Coaxial cable antennas 16 are further spaced a fraction of a wavelength,e.g., half of a wavelength, apart from one another to achieve spatialdiversity. Coaxial cable antennas 16 may, for example, be spacedone-quarter of a wavelength apart from one another. In this manner,coaxial cable antennas 16 receive signals from IMD 12 over multiplereceive paths, providing programmer 10 with spatial and polarizationdiversity, and thereby reducing multi-path propagation interference andantenna nulls. In contrast to wands and other programmer heads that aregenerally placed in close proximity to the body of the patient tocommunicate with IMD 12, the diversity arrangement of coaxial cableantennas 16, e.g., the spatial and polarization diversity, enablereception of signals from IMD 12 over extended distances such as severalfeet or meters from the IMD 12

Coaxial cable antennas 16 are attached to connectors 42 in order toconductively connect coaxial cable antennas 16 with RF module 31. Morespecifically, connectors 42 connect a center conductor of coaxial cableantennas 16 with receiver 32 or transmitter 34 via RSSI 35. In thismanner, signals received by coaxial cable antennas 16 from IMD 12 arerelayed to RF module 31 and signals from RF module 31 are relayed tocoaxial cable antennas 16 for transmission to IMD 12.

FIG. 4 is a schematic diagram illustrating a coaxial cable antenna 16 infurther detail. Coaxial cable antenna 16 is connected via a connector 40to RF module 31 and, more particularly, to receiver 32, transmitter 34or a transceiver of RF module 31. Coaxial cable antenna 16 includes afirst portion 46 and a second portion 48 that are substantiallyperpendicular to one another to provide polarity diversity. As describedabove, portion 46 of coaxial cable antenna 16 is substantially parallelwith a side of display 20 and portion 48 of coaxial cable antenna 16 issubstantially parallel with a top of display 20. In this manner, coaxialcable antenna 16 radiate and tune signals with different polarizations,which permits display 20 to be oriented in numerous ways with respect toIMD 12. More specifically, portion 46 provides coaxial cable antenna 16with a horizontal elliptical or circular polarization, while portion 48of coaxial cable antenna 16 provides a vertical elliptical or circularpolarization.

Coaxial cable antenna 16 includes a center conductor 56 that carriessignals received from IMD 12 or signals to be transmitted to IMD 12. Aninsulator 58 and an outer conductive cladding 60 surround centerconductor 56. Insulator 58 isolates center conductor 56 from electricalinterference as well as from outer conductive cladding 60. The thicknessof insulator 58 varies depending on the type of coaxial cable used toconstruct coaxial cable antennas 16 and provides coaxial cable antennas16 with a characteristic impedance. Conductive cladding 60 may serve asa ground in order to reduce the amount of electrical and radio frequencyinterference experienced by center conductor 56. Center conductor 56 andconductive cladding 60 may be constructed of conductive materials suchas copper, platinum, aluminum and the like. Insulator 58 may beconstructed of materials such as PTFE, polyvinyl, polypropylene or thelike.

As illustrated in the example of FIG. 4, a portion of outer conductivecladding 60 is removed to expose insulator 58 of coaxial cable antenna16. The portion of outer conductive cladding 60 that is removed may belocated at a midpoint of coaxial cable antenna 16. In the example ofFIG. 4, the portion of outer conductive cladding 60 is removed near therespective upper corner of display 20, i.e., proximate the intersectionof portion 46 of coaxial cable antenna 16 that is substantially parallelwith a side of display 20 and portion 48 of coaxial cable antenna 16that is substantially parallel with a top of display 20.

Further, a portion of exposed insulator 58 is removed to expose centerconductor 56 of coaxial cable antenna 16. In the example illustrated inFIG. 4, the portion of insulator 58 removed is approximately at amidpoint of coaxial cable antenna 16, i.e., near the respective uppercorner of display 20. A resistor 62 and a capacitor 64 are coupled tocenter conductor 56. More particularly, resistor 62 and capacitor 64 areconnected between center conductor 56 and outer conductive cladding 60.Capacitor 64 connects to center conductor 56 in order to adjust thevoltage standing wave ratio (VSWR) at the center of an operatingfrequency of coaxial cable antenna 16. Resistor 62 connects to centerconductor 56 to lower the quality factor (Q) of coaxial cable antenna16, in turn, widening the antenna bandwidth in order to achieve simplermatching of coaxial cable antenna 16 and receiver 32 and/or transmitter34 of RF module 31.

Coaxial cable antenna 16 further includes an end portion 68, whichexposes center conductor 56. Coaxial cable antenna 16 can be shear cutto give coaxial cable antenna 16 a particular length. Coaxial cableantenna 16 further includes a hole 66 cutting open center conductor 56to tune the operating frequency of coaxial cable antenna 16. Hole 66 maybe formed, for example, by drilling through coaxial cable antenna 16until center conductor 56 is cut, but stopping before drilling throughthe other side of outer conductive cladding 60. Hole 66 may be locatedbetween end portion 68 and the removed portion of outer conductivecladding 60. Placement of hole 66 nearer end portion 68 results in alower operating frequency than placement of hole 66 near the removedportion of outer conductive cladding 60. Hole 66 may be placed such thatthe operating frequency of coaxial cable antenna 16 is approximately 400Megahertz (MHz) and, more specifically, approximately 403 MHz. Thelength of each coaxial cable antennas 16 is based on the desiredoperating frequency of coaxial cable antennas 16.

Various embodiments of the invention have been described. For example,coaxial cable antennas 16 may be located within a patient monitor thatdoes not have programming capabilities. Coaxial cable antennas 16 may belocated within a separate device and attached to programmer 10 via acable or other connection. Further, although described in terms of anoperating frequency of approximately 400 MHz, the coaxial cable antennasof the invention may be scaled in size to operate at differentfrequencies. These and other embodiments are within the scope of thefollowing claims.

1. A device to communicate with an implanted medical device, the devicecomprising: a first coaxial cable antenna; a second coaxial cableantenna; and a receiver that receives signals from the implanted medicaldevice via at least one of the first and second coaxial cable antennas.2. The device of claim 1, further comprising a transmitter thattransmits signals to the implanted medical device via at least one ofthe first and second coaxial cable antennas.
 3. The device of claim 1,further comprising a display to convey data received from the implantedmedical device to a user.
 4. The device of claim 3, wherein the displayincludes a display housing, and the coaxial cable antennas are mountedwithin the housing.
 5. The device of claim 4, wherein the first andsecond coaxial cable antennas are located in apposition to one another.6. The device of claim 5, wherein each of the coaxial cable antennasincludes a first portion in substantially parallel orientation with aside of the display and a second portion in substantially parallelorientation with another side of the display.
 7. The device of claim 1,wherein each of the coaxial cable antennas includes an outer conductivecladding, and a portion of the outer conductive cladding is removed toexpose an insulator of the coaxial cable antenna.
 8. The device of claim7, wherein each of the coaxial cable antennas includes a centerconductor, and wherein a portion of the exposed insulator is removed toexpose the center conductor of the coaxial cable antenna.
 9. The deviceof claim 8, further comprising a resistor connected between the exposedcenter conductor of the coaxial cable antenna and the outer conductivecladding of the coaxial cable antenna.
 10. The device of claim 8,further comprising a capacitor connected between the exposed centerconductor of the coaxial cable antenna and the outer conductive claddingof the coaxial cable antenna.
 11. The device of claim 1, wherein each ofthe coaxial cable antennas comprises a hole that extends partiallythrough coaxial cable antenna to cut through the center conductor of thecoaxial cable antennas in order to tune an operating frequency of theantenna.
 12. The device of claim 1, wherein each of the coaxial cableantennas includes an center portion that exposes a center conductor ofthe coaxial cable antenna.
 13. The device of claim 1, wherein thecoaxial cable antennas are spaced a fraction of a wavelength apart fromone another to achieve spatial diversity.
 14. The device of claim 13,wherein the coaxial cable antennas are spaced substantially one-half ofa wavelength apart from one another to achieve spatial diversity. 15.The device of claim 1, wherein an operating frequency of the coaxialcable antennas is approximately 403 megahertz.
 16. The device of claim1, wherein the device comprises a programmer for the implanted medicaldevice.
 17. The device of claim 1, wherein the device comprises apatient monitor for the implanted medical device.
 18. A device tocommunicate with an implanted medical device, the device comprising: aplurality of coaxial cable antennas; a receiver to receive signals fromthe implanted medical device via at least one of the coaxial cableantennas; and a device housing, the coaxial cable antennas mountedwithin the device housing.